1. Field of the Invention
The present invention relates to a lens barrel, and particularly, to a lens barrel having a radially-retractable optical element which is capable of radially retracting away from a photographing optical axis position to a radially-retracted position.
2. Description of the Related Art
Generally, in a telescoping lens barrel in which a photographing optical axis is not deflected by use of a mirror or a prism, the length of the lens barrel in the retracted (accommodated) state thereof cannot be made shorter than the total thickness of the optical elements of the photographing optical system in the optical axis direction thereof. Nevertheless, there has been a demand for a further reduction in length of the retracted photographic lens to achieve an extra-short photographic lens. As a solution to this demand, the assignee of the prevent invention has proposed a zoom lens whose length, in a retracted state, is further reduced by radially retracting a part of the photographing optical system away from the photographing optical axis thereof. This zoom lens is disclosed in United States Patent Publication No. US2003/0156832 A1.
In the above-described zoom lens barrel, a part of the optical system is radially retracted to an off-optical-axis position (radially-retracted position). In this case, the radially-retracted optical element is required to be moved with high precision. Particularly, if the optical element is radially retracted by utilizing the rotational driving force of a helicoid ring, a cam ring, or other components in the lens barrel, the timing of the retracting movement must be properly adjusted, otherwise, the proper retracting movement may be interfered with by other optical elements, or the mechanism may be damaged.